Methods and apparatuses for communicating in television white space (TVWS) based on TVWS enablement signal

ABSTRACT

Certain aspects of the present disclosure relate to techniques for supporting television white space (TVWS) communication. In an aspect of the present disclosure, a low-rate TVWS enabler (Mode II wireless communication device) may provide initial enablement for all Mode I devices (e.g., access points and user terminals), as well as it may transmit a contact verification signal (CVS) on a regular basis to keep the Mode I devices enabled for the TVWS communication.

CROSS REFERENCE TO RELATED APPLICATIONS

The present Application for Patent is related by subject matter to U.S.patent application, entitled, “METHODS AND APPARATUSES FOR LOW-RATETELEVISION WHITE SPACE (TVWS) ENABLEMENT”, filed Jan. 12, 2012 andassigned to the assignee hereof and hereby expressly incorporated byreference herein.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present Application for Patent claims benefit of U.S. ProvisionalPatent Application Ser. No. 61/433,046, entitled, “Low-rate TelevisionWhite Space (TVWS) enabler”, filed Jan. 14, 2011 and assigned to theassignee hereof and hereby expressly incorporated by reference herein.

BACKGROUND

Field

Certain aspects of the present disclosure generally relate to wirelesscommunications and, more particularly, to methods and apparatuses forsupporting television white space (TVWS) communication.

Background

Wireless communication networks are widely deployed to provide variouscommunication services such as voice, video, packet data, messaging,broadcast, etc. These wireless networks may be multiple-access networkscapable of supporting multiple users by sharing the available networkresources. Examples of such multiple-access networks include CodeDivision Multiple Access (CDMA) networks, Time Division Multiple Access(TDMA) networks, Frequency Division Multiple Access (FDMA) networks,Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA)networks.

In order to address the issue of increasing bandwidth requirementsdemanded for wireless communications systems, different schemes arebeing developed. One of the schemes, for example, entails expandingWi-Fi technology to utilize the unused frequency spectrum in thetelevision (TV) band (i.e., the TV white space). The Institute ofElectrical and Electronics Engineers (IEEE) 802.11af task group has beenformed to define an amendment to the IEEE 802.11 standard for operatingin the TV white space (TVWS). The IEEE 802.11 standard denotes aWireless Local Area Network (WLAN) air interface standard developed bythe IEEE 802.11 working group for short-range communications (e.g., tensof meters to a few hundred meters). By using the TVWS with frequenciesbelow 1 GHz, IEEE 802.11af may offer greater propagation distances to beachieved, in addition to the increased bandwidth offered by the unusedfrequencies in the TV spectrum.

The Federal Communications Commission (FCC) had developed regulationsfor unlicensed operation in unused TV channels, referred to as TV whitespace (TVWS). The TV white space devices (WSDs), also referred to by theFCC as TV band devices (TVBDs), may need to meet a number ofrequirements for operation in the TVWS so as to avoid causing harmfulinterference to the licensed services in the TV bands (e.g., broadcastTV, wireless microphones, etc).

There are several classes of devices defined by the FCC: fixed andpersonal/portable devices (referred to as portable devices in thisdisclosure). There are two classes of portable devices: Mode I and ModeII devices.

The portable Mode II devices may need to have geo-location capabilitywith an accuracy of 50 meters and may need to have Internet access so asto be able to check with a database to find out which channels in itslocation are white space and available for use. The Mode I devices maynot need to have geo-location capability or Internet access, but theycan only be permitted to transmit in TV channels which are indicated asavailable from a Fixed or Mode II device. In addition, the Mode I deviceafter receiving initial enablement from the Fixed or Mode II device mayneed to receive a “contact verification signal” (CVS) from the Fixed orMode II device at least every 60 seconds in order to continue the TVWScommunication, or the Mode I device may need to cease transmission.

The FCC specifies limits on both the total transmit power, and on thepower spectral density (PSD) of the TV white space devices. The maximumtransmit power of a portable device can be 20 dBm, and this limit can belowered to 16 dBm when the portable device is operating on a channeladjacent to a broadcast TV signal. In addition to the power limit, theremay be also a PSD limit specified by the FCC, which can be controlled bylimiting the maximum power in any 100 kHz band. For portable devices,the limit can be 2.2 dBm in 100 kHz, which can be lowered to −1.8 dBmwhen operating in a channel adjacent to a TV broadcast signal. The PSDlimit can prevent high power narrowband signals.

SUMMARY

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes determining, at anapparatus, a geographical location of the apparatus, obtaining a list ofchannels of a plurality of television white space (TVWS) channels thatsupport TVWS communication, wherein the channels from the list areavailable for use at the geographical location, generating a signalhaving a data rate capable of reaching a plurality of apparatuses,wherein the signal advertises to the apparatuses an enablement for theTVWS communication, and transmitting the signal to the apparatuses usinga first channel from the list.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a firstcircuit configured to determine a geographical location of theapparatus, a second circuit configured to obtain a list of channels of aplurality of television white space (TVWS) channels that support TVWScommunication, wherein the channels from the list are available for useat the geographical location, a third circuit configured to generate asignal having a data rate capable of reaching a plurality ofapparatuses, wherein the signal advertises to the apparatuses anenablement for the TVWS communication, and a transceiver configured totransmit the signal to the apparatuses using a first channel from thelist.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means fordetermining a geographical location of the apparatus, means forobtaining a list of channels of a plurality of television white space(TVWS) channels that support TVWS communication, wherein the channelsfrom the list are available for use at the geographical location, meansfor generating a signal having a data rate capable of reaching aplurality of apparatuses, wherein the signal advertises to theapparatuses an enablement for the TVWS communication, and means fortransmitting the signal to the apparatuses using a first channel fromthe list.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productincludes a computer-readable medium comprising instructions executableto determine, at an apparatus, a geographical location of the apparatus,obtain a list of channels of a plurality of television white space(TVWS) channels that support TVWS communication, wherein the channelsfrom the list are available for use at the geographical location,generate a signal having a data rate capable of reaching a plurality ofapparatuses, wherein the signal advertises to the apparatuses anenablement for the TVWS communication, and transmit the signal to theapparatuses using a first channel from the list.

Certain aspects of the present disclosure provide an access point. Theaccess point generally includes at least one antenna, a first circuitconfigured to determine a geographical location of the access point, asecond circuit configured to obtain a list of channels of a plurality oftelevision white space (TVWS) channels that support TVWS communication,wherein the channels from the list are available for use at thegeographical location, a third circuit configured to generate a signalhaving a data rate capable of reaching a plurality of wireless nodes,wherein the signal advertises to the wireless nodes an enablement forthe TVWS communication, and a transceiver configured to transmit, viathe at least one antenna, the signal to the wireless nodes using a firstchannel from the list.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes searching, at anapparatus, a plurality of television white space (TVWS) channelssupporting TVWS communication for a signal transmitted from anotherapparatus on a first channel of the TVWS channels, wherein the signal iscapable of reaching a plurality of apparatuses for advertising anenablement for the TVWS communication, detecting, based on the search,the signal and the first channel, and transmitting, to the otherapparatus upon the detection, a request for the enablement using thefirst channel.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a firstcircuit configured to search a plurality of television white space(TVWS) channels supporting TVWS communication for a signal transmittedfrom another apparatus on a first channel of the TVWS channels, whereinthe signal is capable of reaching a plurality of apparatuses foradvertising an enablement for the TVWS communication, a second circuitconfigured to detect, based on the search, the signal and the firstchannel, and a transceiver configured to transmit, to the otherapparatus upon the detection, a request for the enablement using thefirst channel.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means forsearching a plurality of television white space (TVWS) channelssupporting TVWS communication for a signal transmitted from anotherapparatus on a first channel of the TVWS channels, wherein the signal iscapable of reaching a plurality of apparatuses for advertising anenablement for the TVWS communication, means for detecting, based on thesearch, the signal and the first channel, and means for transmitting, tothe other apparatus upon the detection, a request for the enablementusing the first channel.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productincludes a computer-readable medium comprising instructions executableto search, at an apparatus, a plurality of television white space (TVWS)channels supporting TVWS communication for a signal transmitted fromanother apparatus on a first channel of the TVWS channels, wherein thesignal is capable of reaching a plurality of apparatuses for advertisingan enablement for the TVWS communication, detect, based on the search,the signal and the first channel, and transmit, to the other apparatusupon the detection, a request for the enablement using the firstchannel.

Certain aspects of the present disclosure provide an access point. Theaccess point generally includes at least one antenna, a first circuitconfigured to search a plurality of television white space (TVWS)channels supporting TVWS communication for a signal transmitted fromanother access point on a first channel of the TVWS channels, whereinthe signal is capable of reaching a plurality of wireless nodes foradvertising an enablement for the TVWS communication, a second circuitconfigured to detect, based on the search, the signal and the firstchannel, and a transceiver configured to transmit, to the other accesspoint upon the detection via the at least one antenna, a request for theenablement using the first channel.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes searching, at anapparatus, a plurality of television white space (TVWS) channelssupporting TVWS communication for a signal transmitted from anotherapparatus on a first channel of the TVWS channels, wherein the signal iscapable of reaching a plurality of apparatuses for advertising anenablement for the TVWS communication, transmitting, to the otherapparatus using the first channel upon detecting the signal and thefirst channel, a request for the enablement, receiving, from the otherapparatus in response to the request, a list of channels of theplurality of TVWS channels being in use by a subset of the apparatuses,and searching, on channels from the list, for a communicating apparatusof the subset.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a firstcircuit configured to search a plurality of television white space(TVWS) channels supporting TVWS communication for a signal transmittedfrom another apparatus on a first channel of the TVWS channels, whereinthe signal is capable of reaching a plurality of apparatuses foradvertising an enablement for the TVWS communication, a transceiverconfigured to transmit, to the other apparatus using the first channelupon detecting the signal and the first channel, a request for theenablement, wherein the transceiver is also configured to receive, fromthe other apparatus in response to the request, a list of channels ofthe plurality of TVWS channels being in use by a subset of theapparatuses, and wherein the first circuit is also configured to search,on channels from the list, for a communicating apparatus of the subset.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means forsearching a plurality of television white space (TVWS) channelssupporting TVWS communication for a signal transmitted from anotherapparatus on a first channel of the TVWS channels, wherein the signal iscapable of reaching a plurality of apparatuses for advertising anenablement for the TVWS communication, means for transmitting, to theother apparatus using the first channel upon detecting the signal andthe first channel, a request for the enablement, means for receiving,from the other apparatus in response to the request, a list of channelsof the plurality of TVWS channels being in use by a subset of theapparatuses; and means for searching, on channels from the list, for acommunicating apparatus of the subset.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productincludes a computer-readable medium comprising instructions executableto search, at an apparatus, a plurality of television white space (TVWS)channels supporting TVWS communication for a signal transmitted fromanother apparatus on a first channel of the TVWS channels, wherein thesignal is capable of reaching a plurality of apparatuses for advertisingan enablement for the TVWS communication, transmit, to the otherapparatus using the first channel upon detecting the signal and thefirst channel, a request for the enablement, receive, from the otherapparatus in response to the request, a list of channels of theplurality of TVWS channels being in use by a subset of the apparatuses,and search, on channels from the list, for a communicating apparatus ofthe subset.

Certain aspects of the present disclosure provide an access terminal.The access terminal generally includes at least one antenna, a firstcircuit configured to search a plurality of television white space(TVWS) channels supporting TVWS communication for a signal transmittedfrom an access point on a first channel of the TVWS channels, whereinthe signal is capable of reaching a plurality of wireless nodes foradvertising an enablement for the TVWS communication, a transceiverconfigured to transmit, via the at least one antenna to the access pointusing the first channel upon detecting the signal and the first channel,a request for the enablement, wherein the transceiver is also configuredto receive, via the at least one antenna from the access point inresponse to the request, a list of channels of the plurality of TVWSchannels being in use by a subset of the wireless nodes, and wherein thefirst circuit is also configured to search, on channels from the list,for another access point of the subset

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective aspects.

FIG. 1 illustrates a wireless communications network in accordance withcertain aspects of the present disclosure.

FIG. 2 illustrates a block diagram of an example access point and userterminals in accordance with certain aspects of the present disclosure.

FIG. 3 illustrates a block diagram of an example wireless device inaccordance with certain aspects of the present disclosure.

FIG. 4 illustrates an example deployment of low-rate television whitespace (TVWS) enabler, Mode I access points and Mode I user stations inaccordance with certain aspects of the present disclosure.

FIG. 5 illustrates an example list of occupied TVWS channels inaccordance with certain aspects of the present disclosure.

FIG. 6 illustrates example frequencies occupied by a low-rate TVWSenabler in accordance with certain aspects of the present disclosure.

FIG. 7 illustrates example operations that may be performed at alow-rate TVWS enabler in accordance with certain aspects of the presentdisclosure.

FIG. 7A illustrates example operations that may be performed at alow-rate TVWS enabler using example components in accordance withcertain aspects of the present disclosure.

FIG. 8 illustrates other example operations that may be performed at aMode I access point in accordance with certain aspects of the presentdisclosure.

FIG. 8A illustrates example operations that may be performed at a Mode Iaccess point using example components in accordance with certain aspectsof the present disclosure.

FIG. 9 illustrates example operations that may be performed at a Mode Iuser station in accordance with certain aspects of the presentdisclosure.

FIG. 9A illustrates example operations that may be performed at a Mode Iuser station using example components in accordance with certain aspectsof the present disclosure.

FIG. 10 illustrates an example procedure of access points transmittingClear-to-send (CTS)-to-Self frames to cover transmission of an enablingframe (EF) or a contact verification signal in accordance with certainaspects of the present disclosure.

FIG. 11 illustrates an example of periodic contact verification signal(CVS) message, traffic indication map (TIM) messages and deliverytraffic indication map (DTIM) message in accordance with certain aspectsof the present disclosure.

DETAILED DESCRIPTION

Various aspects of the disclosure are described more fully hereinafterwith reference to the accompanying drawings. This disclosure may,however, be embodied in many different forms and should not be construedas limited to any specific structure or function presented throughoutthis disclosure. Rather, these aspects are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art. Based on theteachings herein one skilled in the art should appreciate that the scopeof the disclosure is intended to cover any aspect of the disclosuredisclosed herein, whether implemented independently of or combined withany other aspect of the disclosure. For example, an apparatus may beimplemented or a method may be practiced using any number of the aspectsset forth herein. In addition, the scope of the disclosure is intendedto cover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the disclosure set forth herein. Itshould be understood that any aspect of the disclosure disclosed hereinmay be embodied by one or more elements of a claim.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any aspect described herein as “exemplary”is not necessarily to be construed as preferred or advantageous overother aspects.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

An Example Wireless Communication System

The techniques described herein may be used for various wirelesscommunication systems, including communication systems that are based onan orthogonal multiplexing scheme. Examples of such communicationsystems include Spatial Division Multiple Access (SDMA), Time DivisionMultiple Access (TDMA), Orthogonal Frequency Division Multiple Access(OFDMA) systems, Single-Carrier Frequency Division Multiple Access(SC-FDMA) systems, and so forth. An SDMA system may utilize sufficientlydifferent directions to simultaneously transmit data belonging tomultiple user terminals. A TDMA system may allow multiple user terminalsto share the same frequency channel by dividing the transmission signalinto different time slots, each time slot being assigned to differentuser terminal. An OFDMA system utilizes orthogonal frequency divisionmultiplexing (OFDM), which is a modulation technique that partitions theoverall system bandwidth into multiple orthogonal sub-carriers. Thesesub-carriers may also be called tones, bins, etc. With OFDM, eachsub-carrier may be independently modulated with data. An SC-FDMA systemmay utilize interleaved FDMA (IFDMA) to transmit on sub-carriers thatare distributed across the system bandwidth, localized FDMA (LFDMA) totransmit on a block of adjacent sub-carriers, or enhanced FDMA (EFDMA)to transmit on multiple blocks of adjacent sub-carriers. In general,modulation symbols are created in the frequency domain with OFDM and inthe time domain with SC-FDMA.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of wired or wireless apparatuses (e.g.,nodes). In some aspects, a node comprises a wireless node. Such wirelessnode may provide, for example, connectivity for or to a network (e.g., awide area network such as the Internet or a cellular network) via awired or wireless communication link. In some aspects, a wireless nodeimplemented in accordance with the teachings herein may comprise anaccess point or an access terminal.

An access point (“AP”) may comprise, be implemented as, or known asNodeB, Radio Network Controller (“RNC”), eNodeB, Base Station Controller(“BSC”), Base Transceiver Station (“BTS”), Base Station (“BS”),Transceiver Function (“TF”), Radio Router, Radio Transceiver, BasicService Set (“BSS”), Extended Service Set (“ESS”), Radio Base Station(“RBS”), or some other terminology. In some implementations, an accesspoint may comprise a set top box kiosk, a media center, or any othersuitable device that is configured to communicate via a wireless orwired medium. According to certain aspects of the present disclosure,the access point may operate in accordance with the Institute ofElectrical and Electronics Engineers (IEEE) 802.11 family of wirelesscommunications standards.

An access terminal (“AT”) may comprise, be implemented as, or known asan access terminal, a subscriber station, a subscriber unit, a mobilestation, a remote station, a remote terminal, a user terminal, a useragent, a user device, user equipment, a user station, or some otherterminology. In some implementations, an access terminal may comprise acellular telephone, a cordless telephone, a Session Initiation Protocol(“SIP”) phone, a wireless local loop (“WLL”) station, a personal digitalassistant (“PDA”), a handheld device having wireless connectioncapability, a Station (“STA”), or some other suitable processing deviceconnected to a wireless modem. Accordingly, one or more aspects taughtherein may be incorporated into a phone (e.g., a cellular phone or smartphone), a computer (e.g., a laptop), a portable communication device, aportable computing device (e.g., a personal data assistant), a tablet,an entertainment device (e.g., a music or video device, or a satelliteradio), a television display, a flip-cam, a security video camera, adigital video recorder (DVR), a global positioning system device, or anyother suitable device that is configured to communicate via a wirelessor wired medium. According to certain aspects of the present disclosure,the access terminal may operate in accordance with the IEEE 802.11family of wireless communications standards.

FIG. 1 illustrates a multiple-access multiple-input multiple-output(MIMO) system 100 with access points and user terminals. For simplicity,only one access point 110 is shown in FIG. 1. An access point isgenerally a fixed station that communicates with the user terminals andmay also be referred to as a base station or some other terminology. Auser terminal may be fixed or mobile and may also be referred to as amobile station, a wireless device, or some other terminology. Accesspoint 110 may communicate with one or more user terminals 120 at anygiven moment on the downlink and uplink. The downlink (i.e., forwardlink) is the communication link from the access point to the userterminals, and the uplink (i.e., reverse link) is the communication linkfrom the user terminals to the access point. A user terminal may alsocommunicate peer-to-peer with another user terminal. A system controller130 couples to and provides coordination and control for the accesspoints.

While portions of the following disclosure will describe user terminals120 capable of communicating via Spatial Division Multiple Access(SDMA), for certain aspects, the user terminals 120 may also includesome user terminals that do not support SDMA. Thus, for such aspects, anAP 110 may be configured to communicate with both SDMA and non-SDMA userterminals. This approach may conveniently allow older versions of userterminals (“legacy” stations) to remain deployed in an enterprise,extending their useful lifetime, while allowing newer SDMA userterminals to be introduced as deemed appropriate.

The system 100 employs multiple transmit and multiple receive antennasfor data transmission on the downlink and uplink. The access point 110is equipped with N_(ap) antennas and represents the multiple-input (MI)for downlink transmissions and the multiple-output (MO) for uplinktransmissions. A set of K selected user terminals 120 collectivelyrepresents the multiple-output for downlink transmissions and themultiple-input for uplink transmissions. For pure SDMA, it is desired tohave N_(ap)—≧K≧1 if the data symbol streams for the K user terminals arenot multiplexed in code, frequency or time by some means. K may begreater than N_(ap) if the data symbol streams can be multiplexed usingTDMA technique, different code channels with CDMA, disjoint sets ofsubbands with OFDM, and so on. Each selected user terminal transmitsuser-specific data to and/or receives user-specific data from the accesspoint. In general, each selected user terminal may be equipped with oneor multiple antennas (i.e., N_(ut)≧1). The K selected user terminals canhave the same or different number of antennas.

The SDMA system may be a time division duplex (TDD) system or afrequency division duplex (FDD) system. For a TDD system, the downlinkand uplink share the same frequency band. For an FDD system, thedownlink and uplink use different frequency bands. MIMO system 100 mayalso utilize a single carrier or multiple carriers for transmission.Each user terminal may be equipped with a single antenna (e.g., in orderto keep costs down) or multiple antennas (e.g., where the additionalcost can be supported). The system 100 may also be a TDMA system if theuser terminals 120 share the same frequency channel by dividingtransmission/reception into different time slots, each time slot beingassigned to different user terminal 120.

FIG. 2 illustrates a block diagram of access point 110 and two userterminals 120 m and 120 x in MIMO system 100. Access point 110 isequipped with N_(ap) antennas 224 a through 224 ap. User terminal 120 mis equipped with N_(ut,m) antennas 252 ma through 252 mu, and userterminal 120 x is equipped with N_(ut,x) antennas 252 xa through 252 xu.Access point 110 is a transmitting entity for the downlink and areceiving entity for the uplink. Each user terminal 120 is atransmitting entity for the uplink and a receiving entity for thedownlink. As used herein, a “transmitting entity” is an independentlyoperated apparatus or device capable of transmitting data via afrequency channel, and a “receiving entity” is an independently operatedapparatus or device capable of receiving data via a frequency channel.In the following description, the subscript “dn” denotes the downlink,the subscript “up” denotes the uplink, N_(up) user terminals areselected for simultaneous transmission on the uplink, N_(dn) userterminals are selected for simultaneous transmission on the downlink,N_(up) may or may not be equal to N_(dn), and N_(up) and N_(dn) may bestatic values or can change for each scheduling interval. Thebeam-steering or some other spatial processing technique may be used atthe access point and user terminal.

On the uplink, at each user terminal 120 selected for uplinktransmission, a TX data processor 288 receives traffic data from a datasource 286 and control data from a controller 280. TX data processor 288processes (e.g., encodes, interleaves, and modulates) the traffic data{d_(up,m)} for the user terminal based on the coding and modulationschemes associated with the rate selected for the user terminal andprovides a data symbol stream {s_(up,m)}. A TX spatial processor 290performs spatial processing on the data symbol stream {s_(up,m)} andprovides N_(ut,m) transmit symbol streams for the N_(ut,m) antennas.Each transmitter unit (TMTR) 254 receives and processes (e.g., convertsto analog, amplifies, filters, and frequency upconverts) a respectivetransmit symbol stream to generate an uplink signal. N_(ut,m)transmitter units 254 provide N_(ut,m) uplink signals for transmissionfrom N_(ut,m) antennas 252 to the access point 110.

A number N_(up) of user terminals may be scheduled for simultaneoustransmission on the uplink. Each of these user terminals performsspatial processing on its data symbol stream and transmits its set oftransmit symbol streams on the uplink to the access point.

At access point 110, N_(ap) antennas 224 a through 224 ap receive theuplink signals from all N_(up) user terminals transmitting on theuplink. Each antenna 224 provides a received signal to a respectivereceiver unit (RCVR) 222. Each receiver unit 222 performs processingcomplementary to that performed by transmitter unit 254 and provides areceived symbol stream. An RX spatial processor 240 performs receiverspatial processing on the N_(ap) received symbol streams from N_(ap)receiver units 222 and provides N_(up) recovered uplink data symbolstreams. The receiver spatial processing is performed in accordance withthe channel correlation matrix inversion (CCMI), minimum mean squareerror (MMSE), successive interference cancellation (SIC), or some othertechnique. Each recovered uplink data symbol stream {s_(ut,m)} is anestimate of a data symbol stream {s_(up,m)} transmitted by a respectiveuser terminal. An RX data processor 242 processes (e.g., demodulates,deinterleaves, and decodes) each recovered uplink data symbol stream{s_(up,m)} in accordance with the rate used for that stream to obtaindecoded data. The decoded data for each user terminal may be provided toa data sink 244 for storage and/or a controller 230 for furtherprocessing.

On the downlink, at access point 110, a TX data processor 210 receivestraffic data from a data source 208 for N_(dn) user terminals scheduledfor downlink transmission, control data from a controller 230, andpossibly other data from a scheduler 234. The various types of data maybe sent on different transport channels. TX data processor 210 processes(e.g., encodes, interleaves, and modulates) the traffic data for eachuser terminal based on the rate selected for that user terminal TX dataprocessor 210 provides N_(dn) downlink data symbol streams for theN_(dn) user terminals. A TX spatial processor 220 performs spatialprocessing on the N_(dn) downlink data symbol streams, and providesN_(ap) transmit symbol streams for the N_(ap) antennas. Each transmitterunit (TMTR) 222 receives and processes a respective transmit symbolstream to generate a downlink signal. N_(ap) transmitter units 222provide N_(ap) downlink signals for transmission from N_(ap) antennas224 to the user terminals.

At each user terminal 120, N_(ut,m) antennas 252 receive the N_(ap)downlink signals from access point 110. Each receiver unit (RCVR) 254processes a received signal from an associated antenna 252 and providesa received symbol stream. An RX spatial processor 260 performs receiverspatial processing on N_(ut,m) received symbol streams from N_(ut,m)receiver units 254 and provides a recovered downlink data symbol stream{s_(dn,m)} for the user terminal. The receiver spatial processing isperformed in accordance with the CCMI, MMSE, or some other technique. AnRX data processor 270 processes (e.g., demodulates, deinterleaves, anddecodes) the recovered downlink data symbol stream to obtain decodeddata for the user terminal.

At each user terminal 120, N_(ut,m) antennas 252 receive the N_(ap)downlink signals from access point 110. Each receiver unit (RCVR) 254processes a received signal from an associated antenna 252 and providesa received symbol stream. An RX spatial processor 260 performs receiverspatial processing on N_(ut,m) received symbol streams from N_(ut,m)receiver units 254 and provides a recovered downlink data symbol stream{s_(dn,m)} for the user terminal. The receiver spatial processing isperformed in accordance with the CCMI, MMSE, or some other technique. AnRX data processor 270 processes (e.g., demodulates, deinterleaves, anddecodes) the recovered downlink data symbol stream to obtain decodeddata for the user terminal.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice 302 that may be employed within the system 100. The wirelessdevice 302 is an example of a device that may be configured to implementthe various methods described herein. The wireless device 302 may be anaccess point 110 or a user terminal 120.

The wireless device 302 may include a processor 304 which controlsoperation of the wireless device 302. The processor 304 may also bereferred to as a central processing unit (CPU). Memory 306, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 304. A portion of thememory 306 may also include non-volatile random access memory (NVRAM).The processor 304 typically performs logical and arithmetic operationsbased on program instructions stored within the memory 306. Theinstructions in the memory 306 may be executable to implement themethods described herein.

The wireless device 302 may also include a housing 308 that may includea transmitter 310 and a receiver 312 to allow transmission and receptionof data between the wireless device 302 and another wireless node (e.g.,another wireless node in a remote location). The transmitter 310 andreceiver 312 may be combined into a transceiver 314. A plurality oftransmit antennas 316 may be attached to the housing 308 andelectrically coupled to the transceiver 314. The wireless device 302 mayalso include (not shown) multiple transmitters, multiple receivers, andmultiple transceivers.

The wireless device 302 may also include a signal detector 318 that maydetect and quantify the level of signals received by the transceiver314. The signal detector 318 may quantify detection of such signalsusing total energy, energy per subcarrier per symbol, power spectraldensity and/or other quantification metrics. The wireless device 302 mayalso include a digital signal processor (DSP) 320 for use in processingsignals.

The various components of the wireless device 302 may be coupled by abus system 322, which may include a power bus, a control signal bus, anda status signal bus in addition to a data bus.

Certain aspects of the present disclosure can be applied to Wi-Fitechnology. Other wireless technologies can also have similar issues inthe television white space (TVWS).

In order to provide good coverage within a building, one or more accesspoints (APs), such as the AP 110 from FIGS. 1-2 and/or the wirelessdevice 302 from FIG. 3, may need to be installed throughout thebuilding. To obtain good coverage of the building, these APs may need tobe placed towards the middle of the building and not just on the edge ofthe building, near a window. However, this may be a problem since theseAPs may typically need to be Mode II devices with geo-locationcapability and access to the TVWS database. These APs may then enablethe portable Mode I devices (e.g., laptop computer, cell phone, etc.) totransmit in the TVWS. According to certain aspects of the presentdisclosure, the portable Mode I devices may be the user terminals 120illustrated in FIGS. 1-2 and/or the wireless device 302 from FIG. 3.

If the Mode II access points are installed toward the middle of thebuilding, it is possible that they will not be able to obtain GlobalPositioning System (GPS) lock (i.e., to establish GPS connection) with50 meters accuracy. If these Mode II APs cannot maintain GPS lock, thenthe APs cannot transmit and cannot enable the Mode I clients (e.g., theuser terminals 120 from FIGS. 1-2) to transmit. A Mode II device mayneed to check its location every 60 seconds. If geo-location knowledgeis lost, then the network can no longer utilize the TVWS. Furthermore,the loss of GPS lock may bring down the whole network. In some indoorenvironments, the regular GPS may not be sensitive enough to detectenough satellites to calculate the location. Building a high-sensitivityGPS is a possibility, but that may need assisted GPS using a cellularreceiver and massive parallel correlators (e.g., utilizing up to 16,000correlators).

On the other hand, it is very inefficient to place all the Mode II APsnear the edge of the building, where GPS coverage would be possible.This approach may provide very poor coverage and may not provideacceptable network performance. In a home or in an apartment, the ModeII AP may be unusable. In addition, in some applications, the Mode IIdevice may need to be in a certain room if this device performs aspecific function, and hence it may not be possible to place the Mode IIdevice near a window.

Operation in Television White Space (TVWS)

A low-rate TVWS enabler is a novel device whose operation is firstdescribed in the present disclosure. This device is capable of fixingthe problem of AP placement and the problem of loosing GPS connectionfor a floor or even an entire building. According to certain aspects ofthe present disclosure, the TVWS enabler may be configured such as theaccess point 110 from FIGS. 1-2 and/or the wireless device 302 from FIG.3. In an aspect, the low-rate TVWS enabler may comprise the followingfeatures: a GPS receiver (e.g., the receiver 222 from FIG. 2 may operateas a GPS receiver), Internet access, and a low-rate transceiver usingeither direct sequence spread spectrum (DSSS) or OFDM (e.g., thetransceiver TMTR/RCVR 222 from FIG. 2 may operate as a low-rate DSSStransceiver or as a low-rate OFDM transceiver).

According to certain aspects of the present disclosure, the low-rateTVWS enabler device may be placed inside a building near a window wheregood GPS connection can be maintained, e.g., with 50-meter accuracy. Thedevice may also have Internet access so it can operate as a Mode II TVwhite space device. As aforementioned, this device may comprise the lowdata rate DSSS transceiver, wherein the data rate of DSSS signal may bemuch lower than what is typically used by a Wi-Fi access point. Forexample, the data rate may be approximately 10 Kbits per second or 100Kbits per second. However, the signal cannot be a narrowband signalbecause if that were the case the transmit power would be severelylimited based on the FCC regulations on power spectral density limits.Therefore, the low data rate signal may be spread by a higher rate chipsequence to spread the power of the signal out over the majority of the6 MHz TV channel. By utilizing the DSSS, the transmit power may be kepthigh near the power limit, but by keeping the data rate low the coveragecan be made large. As an alternative to employing a DSSS physical (PHY)layer, the low-rate TVWS enabler may utilize an OFDM PHY that usesrepetition codes to lower the data rate of OFDM signal while stillmaintaining the signal bandwidth. Different medium access control (MAC)layer technologies can be utilized with the low-rate PHY, such as theIEEE 802.11 MAC.

By operating at a low data rate, the TVWS enabler may communicate withMode I devices over the entire floor of the building or the entirebuilding. With the low-rate TVWS enabler providing transmissionenablement over the floor or the entire building, TVWS Wi-Fi accesspoints may now operate as Mode I TVWS devices and they may not needgeo-location capability. These Mode I APs may now be placed anywhereinside the buildings where they can receive the enablement signal fromthe low-rate TVWS enabler. In addition, the Wi-Fi client devices (userstations (STAs)) may also receive their enablement signal from thelow-rate TVWS enabler, and not from the access points that providewireless access to the STAs.

In an aspect of the present disclosure, the low-rate TVWS enabler mayprovide initial enablement for all Mode I devices (APs and STAs), aswell as it may transmit a contact verification signal (CVS) on a regularbasis to keep the Mode I devices enabled to continue the TVWS operation.

FIG. 4 illustrates an example deployment 400 of a low-rate TVWS enabler,Mode I access points and Mode I user STAs in accordance with certainaspects of the present disclosure. FIG. 4 illustrates an officebuilding, but the same approach can be applied to any indoor location(e.g., mall, apartment complex, house, etc). For example, in anapartment complex, one low-rate TVWS enabler may enable multipleapartments.

Low-Rate TVWS Enabler

At power up, the low-rate TVWS enabler may establish GPS connection andmay determine its geographical location based on the GPS information.Then, it may contact a TVWS database and obtain a list of available TVchannels at this location. After that, the TVWS enabler may select oneof the available TVWS channel (e.g., Channel A), and may broadcast asignal advertising that it can provide enablement (e.g., an enablementbeacon). In an aspect of the present disclosure, the enablement beaconmay be an IEEE 802.11 beacon with an information element indicating thatthe TVWS enabler provides TVWS enablement. The TVWS enabler may transmitthe enablement advertisement signal using the low-rate PHY so that thetransmitted signal (i.e., the low-rate signal) may be heard over a largeregion (e.g., the entire building). After transmitting the enablementadvertisement signal, the TVWS enabler may wait to be contacted byeither a Mode I AP or a Mode I STA.

If the low-rate enabler operates on a dedicated channel so that none ofthe Mode I APs are operating on that channel, then the low-rate enablermay transmit the enablement beacon frequently so that this beacon can bedetected quickly by a new AP or STA. However, if there are few TVWSchannels, then the low-rate enabler may transmit the enablement beaconless frequently so as to not cause too much interference to the APs/STAsoperating on the same channel. If the low-rate enabler operates on ashared channel, then it may transmit to the APs on that channel aschedule of the enablement beacon so that all the APs/STAs can be silent(i.e., not transmitting) during the enablement beacon so that newAPs/STAs can hear the enablement beacon.

In an aspect of the present disclosure, a Mode I AP may be configured totransmit a “Clear-to-send (CTS)-to-Self” message according to theschedule of enablement beacon. Then, each of the STAs associated withthe AP may be able to receive, on the shared channel, the “CTS-to-Self”message, and refrain from the TVWS communication based on reception ofthe “CTS-to-Self” message.

Once contacted by a Mode I AP/STA, the TVWS enabler may receive the FCCIdentifier (ID) of the Mode I AP/STA, send that FCC ID to the TVWSdatabase for verification, and, after receiving verification, it mayprovide the list of available TV channels to the Mode I AP/STA. Aftertransmitting the list of available channels to the Mode I AP/STA, thelow-rate TVWS enabler may transmit to the Mode I AP/STA the “OccupiedChannel List”. This list may comprise a list of channels that have beenpreviously selected for use by Mode I APs enabled by the low-rateenabler and the channel originally selected for use by the low-rateenabler (e.g., Channel A). The Occupied Channel List may comprise both acenter frequency and a channel bandwidth of a channel, as illustrated inFIG. 5 for three different channels A, B and C. If this is the first APenabled by the low-rate enabler, then the Occupied Channel List may onlycomprise the channel originally selected by the low-rate enabler (e.g.,Channel A).

If the device enabled is a Mode I AP, then the AP may select a channelof operation (e.g., Channel B). After making that selection, the AP maytransmit back to the low-rate enabler that it has selected Channel B foroperation. The low-rate enabler may then add that channel to theOccupied Channel List, i.e., the Occupied Channel List may now compriseChannels A and B.

After the AP has selected its channel of operation, the low-rate enablermay transmit a message to the AP with information about a transmissionperiod of the CVS on that channel. The AP may subsequently utilize thisinformation to wake up STAs that are in a sleep mode so they may be ableto receive the CVS message.

If the device being enabled is a Mode I STA (client), then the STA mayuse the Occupied Channel List to search for an available AP for TVWScommunication. Having this occupied channel list may substantiallyreduce a time required for the STA to discover an AP since there may bemany possible channel center frequencies and bandwidths. Without theOccupied Channel List, searching over all those channel centerfrequencies and bandwidths can be time consuming.

In an aspect of the present disclosure, the low-rate enabler may checkits GPS location every 60 seconds as required by the FCC. In an aspect,the low-rate enabler may check the TVWS database every 24 hours asrequired by the FCC.

Prior to enabling any AP for TVWS communication, the low-rate enablermay only transmit on its originally selected channel (e.g., Channel A).Once the low-rate enabler has enabled the AP, which may be operating ona different channel (e.g., Channel B), the low-rate enabler may need totransmit a CVS periodically as specified by the FCC. In an aspect, thelow-rate enabler may transmit a message to the AP with a schedule forthe CVS signal on that channel (Channel B). In an aspect, the AP mayschedule a quiet time for itself and its associated STAs during thescheduled CVS. Then, the APs and STAs may be able to receive the CVSduring the scheduled time. In an aspect, the low-rate enabler may tuneto the channel occupied by the enabled AP (Channel B), and transmit theCVS on that channel.

In an aspect, the AP may schedule a quiet time for its associated STAsduring the scheduled CVS by transmitting a “CTS-to-Self” messageaccording to the schedule for the CVS signal. Then, each of the STAsassociated with the AP may be able to receive, with the periodicity oftransmitting the CVS from the low-rate TVWS enabler, the “CTS-to-Selfmessage”. That STA may refrain, based on the received “CTS-to-Self”message, from the TVWS communication on the Channel B with the AP duringreception of the CVS.

If multiple APs have been enabled and operate on separate channels, thenthe low-rate enabler may periodically tune to each of the channelsoccupied by an AP and transmit a CVS message. FIG. 6 illustrates anexample of switching between channels (e.g., performed by the low-rateenabler), in the case when combination of the low-rate enabler and allenabled APs can utilize a set of three channels (Channels A, B and C).As illustrates in FIG. 6, the low-rate enabler may cycle through the setof channels with a period of time T. In an aspect, this cycle period maybe a fraction of one minute so that the low-rate enabler may tune toeach channel multiple times in one minute.

For example, as illustrated in FIG. 6, the low-rate enabler may occupyChannel A for a period of time T1 during which it may transmit theenablement advertisement making it possible for new APs and STAs todiscover the low-rate enabler and to obtain initial enablement. Then,low-rate enabler may operate on Channel B for a period of time T2 duringwhich it may transmit the CVS signal so that all the APs and STAsoperating on that channel may be able to receive the CVS signal. Afterthat, the low-rate enabler may operate on Channel C for a period of timeT3 during which it may transmit the CVS signal so that the APs and STAsoperating on Channel C may be able to receive the CVS signal. In anaspect, the time periods T2 and T3 may be much shorter than the timeperiod T1 since the time required to transmit the CVS may not be verylong. In this case, the low-rate enabler may operate much of the time onChannel A where new APs and STAs can discover it.

Mode I Access Point

At power up, a Mode I AP may search each of a plurality of TV channelsfor a low-rate enabler. When the low-rate enabler is detected, then theMode I AP may send to the low-rate enabler a request for enablement on achannel used by the low-rate enabler. Along with the enablement request,the Mode I AP may include its FCC ID. After receiving the list ofavailable TV channels and Occupied Channel List from the low-rateenabler, the Mode I AP may select a channel for use. It is more likelythat the AP will choose a channel not currently occupied by other APs sothat they do not share the same channel, but the Mode I AP may alsochoose a channel in the Occupied Channel List if there are limitednumber of channels to choose from.

After selecting a channel for operation, the Mode I AP may transmit tothe low-rate enabler information about which channel it has selected foroperation (e.g., a center frequency and a bandwidth of the channel). Inan aspect, the Mode I AP may communicate with the low-rate enabler usinga low-rate PHY (e.g., a low-rate OFDM PHY or a low-rate DSSS PHY) inboth transmit and receive directions. After transmitting the channelinformation to the low-rate enabler, the Mode I AP may begin normaloperation on the selected channel. In an aspect of the presentdisclosure, the Mode I AP may schedule a quiet time for itself and allits associated STAs during the CVS schedule.

Periodically, the Mode I AP may receive a CVS signal from the low-rateenabler. If it does not receive the CVS for a time period of more than60 seconds, the AP may switch back to the original channel occupied bythe low-rate enabler (e.g., Channel A), and it may request a new TVWSenablement.

In an aspect of the present disclosure, the Mode I AP may transmit,within a beacon, a frequency of a low-rate enabler. In this way, when anew STA arrives and hears the AP beacon, the STA may know on whichchannel to find the low-rate enabler. This may decrease the time neededby the STA to obtain the initial enablement. In an aspect, the beaconmay also comprise a MAC address of the low-rate enabler.

Mode I User Station (STA)

A Mode I STA may begin its operation by searching for a low-rate enableror a Mode I AP. If the Mode I STA hears a Mode I AP advertising in itsbeacon a frequency of the low-rate enabler, then the STA may tune tothat frequency. Then, once the STA hears an enablement beacontransmitted from the low-rate enabler, the STA may transmit anenablement request on the same channel used by the low-rate enabler,along with its FCC ID. After the STA receives a list of availablechannels and an Occupied Channel List from the low-rate TVWS enabler,the STA may then search for a Mode I AP on the channels listed in theOccupied Channel List. In an aspect of the present disclosure, the ModeI STA may communicate with the low-rate enabler using a low-rate PHY(e.g., a low-rate OFDM PHY or a low-rate DSSS PHY) in both transmit andreceive directions.

Since the STA has already received enablement, it may utilize eitheractive or passive scanning to search for the AP. By using activescanning, the STA may find the AP much faster. After that, the STA mayassociate with the AP for TVWS communication based on one of manycriteria, for example, based on a receive signal strength. Once theassociation procedure with the Mode I AP is completed, the STA mayperform normal operation. In an aspect, the STA may quiet itstransmission during the CVS schedule, which may be received from the AP.Periodically, the STA may receive a CVS signal from the low-rateenabler. If it does not receive the CVS for a period of more than 60seconds, the STA may return to the original channel occupied by thelow-rate enabler (e.g., Channel A) and request a new enablement.

FIG. 7 illustrates example operations 700 that may be performed at alow-rate TVWS enabler (i.e., at a Mode II access point) in accordancewith certain aspects of the present disclosure. At 702, the low-rateTVWS enabler may determine its geographical location. At 704, thelow-rate TVWS enabler may obtain a list of channels of a plurality ofTVWS channels that support TVWS communication, wherein the channels fromthe list may be available for use at the geographical location. At 706,the low-rate TVWS enabler may generate a signal having a data ratecapable of reaching a plurality of apparatuses (e.g., Mode I accesspoints and Mode I stations), wherein the signal may advertise to theapparatuses an enablement for the TVWS communication. At 708, thelow-rate TVWS enabler may transmit the data rate signal to theapparatuses using a first channel from the list. In an aspect, at leastone of the TVWS enabler or the plurality of apparatuses comprises TVBDoperating in the TVWS.

In an aspect of the present disclosure, the low-rate TVWS enabler mayreceive, from a subset of the apparatuses on the first channel, one ormore requests for enabling the TVWS communication at the subset ofapparatuses. Further, the low-rate TVWS enabler may receive an IDassociated with each apparatus from the subset. Then, the low-rate TVWSenabler may transmit, on the first channel in response to the requests,the list of channels to one or more apparatuses from the subset, whereineach of the one or more apparatuses may be associated with the ID thatwas verified.

FIG. 7A illustrates example operations 700A that may be performed at alow-rate TVWS enabler (e.g., at the access point 110 from FIG. 2 and/orat the wireless device 302 from FIG. 3) using example components inaccordance with certain aspects of the present disclosure. At 702A, afirst circuit of the low-rate TVWS enabler (e.g., the controller 230from FIG. 2 and/or the signal detector 318 from FIG. 3) may beconfigured to determine its geographical location. At 704A, a secondcircuit of the low-rate TVWS enabler (e.g., the controller 230 and/orthe signal detector 318) may be configured to obtain a list of channelsof a plurality of TVWS channels that support TVWS communication, whereinthe channels from the list may be available for use at the geographicallocation. At 706A, a third circuit of the low-rate TVWS enabler (e.g.,the TX data processor 210 from FIG. 2 and/or the processor 304 from FIG.3) may be configured to generate a signal having a data rate capable ofreaching a plurality of apparatuses (e.g., Mode I access points and ModeI stations), wherein the signal may advertise to the apparatuses anenablement for the TVWS communication. At 708A, a transceiver of thelow-rate TVWS enabler (e.g., the transceiver 222 from FIG. 2 and/or thetransceiver 314 from FIG. 3) may be configured to transmit the data ratesignal to the apparatuses using a first channel from the list.

FIG. 8 illustrates other example operations 800 that may be performed atan apparatus (e.g., a Mode I access point) in accordance with certainaspects of the present disclosure. At 802, the access point may search aplurality of TVWS channels supporting TVWS communication for a signaltransmitted from another apparatus (e.g., from a low-rate TVWS enabler)on a first channel of the TVWS channels, wherein the signal may becapable of reaching a plurality of apparatuses (e.g., Mode I accesspoints and Mode I stations) for advertising an enablement for the TVWScommunication. At 804, the access point may detect, based on the search,the signal and the first channel. At 806, the access point may transmit,to the other apparatus upon the detection, a request for the enablementusing the first channel. In an aspect, at least one of the apparatus,the other apparatus, or the plurality of apparatuses comprise TVBDoperating in the TVWS.

FIG. 8A illustrates example operations 800A that may be performed at aMode I access point (e.g., at the access point 110 from FIG. 2 and/or atthe wireless device 302 from FIG. 3) using example components inaccordance with certain aspects of the present disclosure. At 802A, afirst circuit of the access point (e.g., the RCVR unit 222 from FIG. 2and/or the receiver 312 from FIG. 3) may be configured to search aplurality of TVWS channels supporting TVWS communication for a signaltransmitted from another apparatus (e.g., from a low-rate TVWS enabler)on a first channel of the TVWS channels, wherein the signal may becapable of reaching a plurality of apparatuses (e.g., Mode I accesspoints and Mode I stations) for advertising an enablement for the TVWScommunication. At 804A, a second circuit of the access point (e.g., theRX data processor 242 from FIG. 2 and/or the signal detector 318 fromFIG. 3) may be configured to detect, based on the search, the signal andthe first channel. At 806A, a transceiver of the access point (e.g., thetransceiver 222 from FIG. 2 and/or the transceiver 314 from FIG. 3) maybe configured to transmit, to the other apparatus upon the detection, arequest for the enablement using the first channel.

FIG. 9 illustrates example operations 900 that may be performed at anapparatus (e.g., a Mode I STA) in accordance with certain aspects of thepresent disclosure. At 902, the STA may search a plurality of TVWSchannels supporting TVWS communication for a signal transmitted fromanother apparatus (e.g., from a low-rate TVWS enabler) on a firstchannel of the TVWS channels, wherein the signal may be capable ofreaching a plurality of apparatuses (e.g., Mode I access points and ModeI STAs) for advertising an enablement for the TVWS communication. At904, the STA may transmit, to the other apparatus using the firstchannel upon detecting the signal and the first channel, a request forthe enablement. At 906, the STA may receive, from the other apparatus inresponse to the request, a list of channels of the plurality of TVWSchannels being in use by a subset of the apparatuses. At 908, the STAmay search, on channels from the list, for a communicating apparatus ofthe subset. In an aspect, at least one of the apparatus, the otherapparatus, or the plurality of apparatuses comprise TVBD operating inthe TVWS.

FIG. 9A illustrates example operations 900A that may be performed at aMode I user station (STA) (e.g., at the user terminal 120 from FIG. 2and/or at the wireless device 302 from FIG. 3) using example componentsin accordance with certain aspects of the present disclosure. At 902A, afirst circuit of the STA (e.g., the RCVR unit 254 from FIG. 2 and/or thereceiver 312 from FIG. 3) may be configured to search a plurality ofTVWS channels supporting TVWS communication for a signal transmittedfrom another apparatus (e.g., from a low-rate TVWS enabler) on a firstchannel of the TVWS channels, wherein the signal may be capable ofreaching a plurality of apparatuses (e.g., Mode I access points and ModeI STAs) for advertising an enablement for the TVWS communication. At904A, a transceiver of the STA (e.g., the transceiver 254 from FIG. 2and/or the transceiver 314 from FIG. 3) may be configured to transmit,to the other apparatus using the first channel upon detecting the signaland the first channel, a request for the enablement. At 906A, thetransceiver of the STA may be also configured to receive, from the otherapparatus in response to the request, a list of channels of theplurality of TVWS channels being in use by a subset of the apparatuses.At 908A, the first circuit of the STA may be also configured to search,on channels from the list, for a communicating apparatus of the subset.

Scheduling of Contact Verification Signal and Enabling Frame

According to certain aspects of the present disclosure, a low rate PHYof low-rate enabler (LRE) may transmit an Enabling Frame (EF) and a CVSas packets in order to enable dependent STAs and/or APs to discover theLRE. However, since the LRE may not be able to detect some of thetransmissions from the enabled devices (since they may be transmitted ata high PHY rate), the LRE may not be able to perform the carrier senseand defer to such transmissions. In an absence of a mechanism fordeferral, a probability of the EF colliding with current transmissionsmay be high. Certain aspects of the present disclosure support a methodfor avoiding collisions of the EF with other network traffic.

FIG. 10 illustrates an example procedure 1000 of access pointstransmitting “CTS-to-Self” frames to cover transmission of an EF or aCVS in accordance with certain aspects of the present disclosure. At afirst step, each AP enabled by the LRE may obtain an interval oftransmission of the EF and the CVS by the LRE. At a second step, at atime instant T before the scheduled arrival of the CVS or EF, the AP maytransmit a “CTS-to-Self” or any other frame with a duration fieldsetting that is long enough to cover at least duration up to andincluding the transmission time of the EF and/or the CVS. In an aspect,the Carrier Sense Multiple Access (CSMA) contention procedure may beutilized for transmission of the “CTS-to-Self” message. In addition, thetime instant T may be equal to a sum of a constant value and a randomvalue to ensure that different APs do not collide in transmitting the“CTS-to-Self” messages. A STA receiving the “CTS-to-Self” message mayrefrain from TVWS communication for a period of time indicated in theduration field.

It should be noted that the EF/CVS may be transmitted by contention, sothe exact time may not be known a priori. Therefore, the APs may set theduration field with sufficient margin to account for the contentiontime. At a last step, once the EF or CVS has been transmitted, the APmay then transmit a Contention-Free End (CF-End) frame to recover any ofthe duration that it may over-reserved. A STA receiving the CF-End framemay be configured to reset its Network Allocation Vector (NAV) counterbased on the received CF-End frame, as illustrated in FIG. 10.

Scheduling of CVS Messages for Station in Power Save Mode

In an aspect of the present disclosure, a low-rate enabler may tune toall the channels of APs that it has enabled to send the CVS signal formaintaining enablement of the APs and STAs. At initial enablement, thelow-rate enabler may send to the AP on each channel the period of theCVS signal on that channel. The AP may use the knowledge of that periodto wake up sleeping STAs, so that they may be able to receive the CVSsignal and maintain their enablement.

In an aspect of the present disclosure, the AP may transmit one or moretraffic indication map (TIM) messages and delivery traffic indicationmap (DTIM) messages on a regular basis. Inside each TIM, a counter maybe present that counts down to the next DTIM. The AP may use thisstructure to schedule transmission of a DTIM immediately beforetransmitting a CVS message. Inside the DTIM message, the AP may set abroadcast bit indicating that a broadcast signal (i.e., the CVS message)will be transmitted. In the TVWS, the STA may wake up to receive the CVSwhen the STA receives the DTIM with the broadcast bit set.

FIG. 11 illustrates an example process 1100 of the periodic CVS message,TIM and DTIM messages. This process may work as follows. An AP mayutilize the DTIM that is just prior to the time of arrival of the CVS toschedule wakening of STAs that are in a sleep state. The AP may set abroadcast bit in the DTIM message. All the STAs may wake up at the DTIM,read the broadcast bit and stay awake until they receive the CVSmessage. In an aspect, the STAs may wake up to listen to some of the TIMmessages and read the down counter to determine when the next DTIM isscheduled.

In an aspect, once the CVS message has been transmitted, the AP maytransmit a broadcast message indicating the CVS has been transmitted.This may permit the STAs to be put back to the sleep state, if there isno other data waiting for them.

The low-rate enabler may execute the above CVS procedure on all thechannels that it has enabled an AP. In an aspect, the times fortransmitting the CVS signals may be offset on each of the channels sothe low-rate enabler may have enough time to tune to each of thechannels.

Low-Rate Physical (PHY) Layer

In accordance with certain aspects of the present disclosure, a low-rateenabler, Mode I APs and Mode I STAs may utilize several possiblelow-rate PHYs in order to provide an initial TVWS communicationenablement and maintain the TVWS enablement with a CVS signal.

In one aspect, a direct sequence spread spectrum (DSSS) PHY with a lowdata rate may provide for long-range operation and a high chip rate tospread the spectrum over the majority of 6 MHz TV channel to permittransmission at close to a maximum transmit power. Another possibilitycan be to use the 1 MHz IEEE 802.11 based PHY with the time scale of themodulation and chipping sequence scaled up by approximately the factorof four so that the data rate may drop to 250 Kb/s and the bandwidth maydrop to approximately 5 MHz. At this data rate, the coverage of this PHYlayer signaling in the TV white space may be large.

According to certain aspects of the present disclosure, a lower datarate may be obtained by decreasing the data rate of the 1 Mbits persecond DSSS 802.11 PHY by a factor of two or four and then scaling from20 MHz down to 5 MHz resulting in a data rate of 125 Kbits per secondand 62.5 Kbits per second, respectively.

According to certain aspects of the present disclosure, a low data ratePHY may be obtained by using a repetition code in an OFDM PHY todecrease the data rate while maintaining the full bandwidth. Otherlow-rate PHY designs may also be possible.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in Figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering. For example, operations 700, 800 and 900 illustratedin FIGS. 7, 8 and 9 correspond to components 700A, 800A and 900Aillustrated in FIGS. 7A, 8A and 9A.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.

For example, the means for determining may comprise an applicationspecific integrated circuit, e.g., the TX data processor 210 from FIG. 2of the access point 110, the RX data processor 242 from FIG. 2 of theaccess point 110, the RX data processor 270 from FIG. 2 of the userterminal 120, the TX data processor 288 from FIG. 2 of the user terminal120, or the processor 304 from FIG. 3 of the wireless device 302. Themeans for obtaining may comprise an application specific integratedcircuit, e.g., the TX data processor 210, the RX data processor 242, theRX data processor 270, the TX data processor 288, or the processor 304.The means for generating may comprise an application specific integratedcircuit, e.g., the TX data processor 210, the RX data processor 242, theRX data processor 270, the TX data processor 288, or the processor 304.The means for transmitting may comprise a transceiver, e.g., thetransceiver 222 from FIG. 2 of the access point 110, the transceiver 254from FIG. 2 of the user terminal 120, or the transmitter 310 from FIG. 3of the wireless device 302. The means for establishing may comprise atransceiver, e.g., the transceiver 222, the transceiver 254, or thetransceiver 314 from FIG. 3 of the wireless device 302. The means forcommunicating may comprise an application specific integrated circuit,e.g., the TX data processor 210, the RX data processor 242, the RX dataprocessor 270, the TX data processor 288, or the processor 304. Themeans for selecting may comprise an application specific integratedcircuit, e.g., the TX data processor 210, the RX data processor 242, theRX data processor 270, the TX data processor 288, or the processor 304.The means for receiving may comprise a transceiver, e.g., thetransceiver 222, the transceiver 254, or the receiver 312 from FIG. 3 ofthe wireless device 302. The means for including may comprise anapplication specific integrated circuit, e.g., the TX data processor210, the RX data processor 242, the RX data processor 270, the TX dataprocessor 288, or the processor 304. The means for tuning may comprisean application specific integrated circuit, e.g., the TX data processor210, the RX data processor 242, the RX data processor 270, the TX dataprocessor 288, or the processor 304. The means for searching maycomprise an application specific integrated circuit, e.g., the TX dataprocessor 210, the RX data processor 242, the RX data processor 270, theTX data processor 288, or the processor 304. The means for detecting maycomprise an application specific integrated circuit, e.g., the TX dataprocessor 210, the RX data processor 242, the RX data processor 270, theTX data processor 288, or the processor 304. The means for continuingmay comprise an application specific integrated circuit, e.g., the TXdata processor 210, the RX data processor 242, the RX data processor270, the TX data processor 288, or the processor 304. The means forswitching may comprise an application specific integrated circuit, e.g.,the TX data processor 210, the RX data processor 242, the RX dataprocessor 270, the TX data processor 288, or the processor 304. Themeans for performing active scanning may comprise an applicationspecific integrated circuit, e.g., the TX data processor 210, the RXdata processor 242, the RX data processor 270, the TX data processor288, or the processor 304. The means for performing passive scanning maycomprise an application specific integrated circuit, e.g., the TX dataprocessor 210, the RX data processor 242, the RX data processor 270, theTX data processor 288, or the processor 304. The means for waking up maycomprise an application specific integrated circuit, e.g., the TX dataprocessor 210, the RX data processor 242, the RX data processor 270, theTX data processor 288, or the processor 304. The means for refrainingmay comprise an application specific integrated circuit, e.g., the TXdata processor 210, the RX data processor 242, the RX data processor270, the TX data processor 288, or the processor 304. The means forreading may comprise an application specific integrated circuit, e.g.,the TX data processor 210, the RX data processor 242, the RX dataprocessor 270, the TX data processor 288, or the processor 304. Themeans for resetting may comprise an application specific integratedcircuit, e.g., the TX data processor 210, the RX data processor 242, theRX data processor 270, the TX data processor 288, or the processor 304.The means for putting may comprise an application specific integratedcircuit, e.g., the TX data processor 210, the RX data processor 242, theRX data processor 270, the TX data processor 288, or the processor 304.The means for modulating may comprise an application specific integratedcircuit, e.g., the TX data processor 210, the TX data processor 288, orthe processor 304.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thepresent disclosure may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in any form of storage medium that is knownin the art. Some examples of storage media that may be used includerandom access memory (RAM), read only memory (ROM), flash memory, EPROMmemory, EEPROM memory, registers, a hard disk, a removable disk, aCD-ROM and so forth. A software module may comprise a singleinstruction, or many instructions, and may be distributed over severaldifferent code segments, among different programs, and across multiplestorage media. A storage medium may be coupled to a processor such thatthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware, or any combination thereof. If implemented in software, thefunctions may be stored or transmitted over as one or more instructionsor code on a computer-readable medium. Computer-readable media includeboth computer storage media and communication media including any mediumthat facilitates transfer of a computer program from one place toanother. A storage medium may be any available medium that can beaccessed by a computer. By way of example, and not limitation, suchcomputer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code in the form of instructions or data structures and that canbe accessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if the software is transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared (IR), radio, and microwave, thenthe coaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. Disk and disc, as used herein, include compactdisc (CD), laser disc, optical disc, digital versatile disc (DVD),floppy disk, and Blu-ray® disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers. Thus, insome aspects computer-readable media may comprise non-transitorycomputer-readable media (e.g., tangible media). In addition, for otheraspects computer-readable media may comprise transitorycomputer-readable media (e.g., a signal). Combinations of the aboveshould also be included within the scope of computer-readable media.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein. For certain aspects, the computer program product may includepackaging material.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition oftransmission medium.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

While the foregoing is directed to aspects of the present disclosure,other and further aspects of the disclosure may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. An apparatus for wireless communications,comprising: a first circuit configured to search a plurality of channelssupporting wireless communication for a signal transmitted from anotherapparatus on a first channel of the channels, wherein the signal iscapable of reaching a plurality of apparatuses for advertising anenablement for the wireless communication; a second circuit configuredto detect, based on the search, the signal and the first channel; and atransceiver configured to transmit, to the other apparatus upon thedetection, a request for the enablement using the first channel.
 2. Theapparatus of claim 1, wherein the transceiver is also configured to:transmit, to the other apparatus, an identifier (ID) of the apparatusalong with the request.
 3. The apparatus of claim 1, wherein theplurality of channels supporting wireless communication comprise aplurality of television white space (TVWS) channels supporting TVWScommunication, and wherein enablement for the wireless communicationcomprises enablement for the TVWS communication.
 4. The apparatus ofclaim 3, wherein the transceiver is also configured to: receive, inresponse to the request, at least one of a first list of channels of theplurality of TVWS channels available for use by the apparatus, or asecond list of channels of the plurality of TVWS channels being in useby a subset of the apparatuses, and the apparatus further comprising athird circuit configured to select, from the at least one of first listor second list, a second channel for the TVWS communication by theapparatus.
 5. The apparatus of claim 4, wherein the transceiver is alsoconfigured to: transmit, to the other apparatus, a center frequency anda bandwidth of the second channel.
 6. The apparatus of claim 4, whereinthe transceiver is also configured to: receive, from the otherapparatus, a message with information about periodicity of transmittinga contact verification signal (CVS) on the second channel; receive, withthe periodicity, the CVS on the second channel; and continue the TVWScommunication on the second channel based on reception of the CVS. 7.The apparatus of claim 6, wherein the transceiver is also configured to:switch from the second channel to the first channel, if the CVS was notreceived for a period of time; and transmit, using the first channel,another request for the enablement.
 8. The apparatus of claim 6, whereinthe transceiver is also configured to: transmit, on the second channelaccording to the periodicity, one or more traffic indication map (TIM)messages and a delivery traffic indication map (DTIM) message before theCVS was transmitted on the second channel from the other apparatus, andwherein each of the TIM messages comprises a counter that counts down tothe transmission of the DTIM message, and the DTIM message istransmitted immediately before the CVS transmission.
 9. The apparatus ofclaim 6, wherein the transceiver is also configured to: transmit, uponreceiving the CVS, a broadcast message indicating that the CVS wastransmitted from the other apparatus.
 10. The apparatus of claim 4,wherein the transceiver is also configured to: receive, from the otherapparatus, a message comprising a schedule of receiving a contactverification signal (CVS) on the second channel; refrain, according tothe schedule, from the TVWS communication on the second channel; receivethe CVS according to the schedule; and continue the TVWS communicationon the second channel after receiving the CVS.
 11. The apparatus ofclaim 10, wherein the transceiver is also configured to: transmit, inresponse to the message, a broadcast message with the schedule to one ormore of the apparatuses associated with the apparatus.
 12. The apparatusof claim 10, wherein the transceiver is also configured to: transmit aContention-Free End (CF-End) frame after the CVS was transmitted fromthe other apparatus.
 13. The apparatus of claim 10, wherein: thetransceiver is also configured to transmit a Clear-to-send (CTS)-to-Selfmessage according to the schedule, and the CTS-to-Self message comprisesa duration field indicating a period of time equal to at least durationof transmitting the CVS from the other apparatus.
 14. The apparatus ofclaim 3, wherein the transceiver is also configured to: receive, on thefirst channel, a message with a schedule of transmitting the signal fromthe other apparatus, if the first channel is used for the TVWScommunication by the apparatus and a subset of the apparatuses; andrefrain from the TVWS communication according to the schedule.
 15. Theapparatus of claim 14, wherein the transceiver is also configured to:transmit, to one or more apparatuses from the subset associated with theapparatus, another message with the schedule.
 16. The apparatus of claim14, wherein: the transceiver is also configured to transmit aClear-to-send (CTS)-to-Self message according to the schedule, and theCTS-to-Self message comprises a duration field indicating a period oftime equal to at least duration of transmitting the signal from theother apparatus.
 17. The apparatus of claim 1, wherein: the signalcomprises a direct sequence spread spectrum (DSSS) signal.
 18. Theapparatus of claim 1, wherein: a data rate of the signal isapproximately 10 Kbits per second or 100 Kbits per second, and abandwidth of the signal is approximately 5 MHz or 6 MHz.
 19. Theapparatus of claim 1, wherein: a data rate of the signal isapproximately 250 Kbits per second, 125 Kbits per second, or 62.5 Kbitsper second, and a bandwidth of the signal is approximately 5 MHz. 20.The apparatus of claim 1, wherein: the transceiver is also configured totransmit a beacon comprising information about the first channel, andthe information comprises at least one of a center frequency of thefirst channel, a bandwidth of the first channel, or an address of theother apparatus.
 21. A method for wireless communications, comprising:searching, at an apparatus, a plurality of channels supporting wirelesscommunication for a signal transmitted from another apparatus on a firstchannel of the channels, wherein the signal is capable of reaching aplurality of apparatuses for advertising an enablement for the wirelesscommunication; detecting, based on the search, the signal and the firstchannel; and transmitting, to the other apparatus upon the detection, arequest for the enablement using the first channel.
 22. The method ofclaim 21, further comprising: transmitting, to the other apparatus, anidentifier (ID) of the apparatus along with the request.
 23. The methodof claim 21, wherein the plurality of channels supporting wirelesscommunication comprise a plurality of television white space (TVWS)channels supporting TVWS communication, and wherein enablement for thewireless communication comprises enablement for the TVWS communication.24. The method of claim 23, further comprising: receiving, in responseto the request, at least one of a first list of channels of theplurality of TVWS channels available for use by the apparatus, or asecond list of channels of the plurality of TVWS channels being in useby a subset of the apparatuses; and selecting, from the at least one offirst list or second list, a second channel for the TVWS communicationby the apparatus.
 25. The method of claim 24, further comprising:transmitting, to the other apparatus, a center frequency and a bandwidthof the second channel.
 26. The method of claim 24, further comprising:receiving, from the other apparatus, a message with information aboutperiodicity of transmitting a contact verification signal (CVS) on thesecond channel; receiving, with the periodicity, the CVS on the secondchannel; and continuing the TVWS communication on the second channelbased on reception of the CVS.
 27. The method of claim 26, furthercomprising: switching from the second channel to the first channel, ifthe CVS was not received for a period of time; and transmitting, usingthe first channel, another request for the enablement.
 28. The method ofclaim 26, further comprising: transmitting, on the second channelaccording to the periodicity, one or more traffic indication map (TIM)messages and a delivery traffic indication map (DTIM) message before theCVS was transmitted on the second channel from the other apparatus,wherein each of the TIM messages comprises a counter that counts down tothe transmission of the DTIM message, and the DTIM message istransmitted immediately before the CVS transmission.
 29. The method ofclaim 26, further comprising: transmitting, upon receiving the CVS, abroadcast message indicating that the CVS was transmitted from the otherapparatus.
 30. The method of claim 24, further comprising: receiving,from the other apparatus, a message comprising a schedule of receiving acontact verification signal (CVS) on the second channel; refraining,according to the schedule, from the TVWS communication on the secondchannel; receiving the CVS according to the schedule; and continuing theTVWS communication on the second channel after receiving the CVS. 31.The method of claim 30, further comprising: transmitting, in response tothe message, a broadcast message with the schedule to one or more of theapparatuses associated with the apparatus.
 32. The method of claim 30,further comprising: transmitting a Contention-Free End (CF-End) frameafter the CVS was transmitted from the other apparatus.
 33. The methodof claim 30, further comprising: transmitting a Clear-to-send(CTS)-to-Self message according to the schedule, wherein the CTS-to-Selfmessage comprises a duration field indicating a period of time equal toat least duration of transmitting the CVS from the other apparatus. 34.The method of claim 23, further comprising: receiving, on the firstchannel, a message with a schedule of transmitting the signal from theother apparatus, if the first channel is used for the TVWS communicationby the apparatus and a subset of the apparatuses; and refraining fromthe TVWS communication according to the schedule.
 35. The method ofclaim 34, further comprising: transmitting, to one or more apparatusesfrom the subset associated with the apparatus, another message with theschedule.
 36. The method of claim 34, further comprising: transmitting aClear-to-send (CTS)-to-Self message according to the schedule, whereinthe CTS-to-Self message comprises a duration field indicating a periodof time equal to at least duration of transmitting the signal from theother apparatus.
 37. The method of claim 21, wherein: the signalcomprises a direct sequence spread spectrum (DSSS) signal.
 38. Themethod of claim 21, wherein: a data rate of the signal is approximately10 Kbits per second or 100 Kbits per second, and a bandwidth of thesignal is approximately 5 MHz or 6 MHz.
 39. The method of claim 21,wherein: a data rate of the signal is approximately 250 Kbits persecond, 125 Kbits per second, or 62.5 Kbits per second, and a bandwidthof the signal is approximately 5 MHz.
 40. The method of claim 21,further comprising: transmitting a beacon comprising information aboutthe first channel, wherein the information comprises at least one of acenter frequency of the first channel, a bandwidth of the first channel,or an address of the other apparatus.
 41. An apparatus for wirelesscommunications, comprising: means for searching a plurality of channelssupporting wireless communication for a signal transmitted from anotherapparatus on a first channel of the channels, wherein the signal iscapable of reaching a plurality of apparatuses for advertising anenablement for the wireless communication; means for detecting, based onthe search, the signal and the first channel; and means fortransmitting, to the other apparatus upon the detection, a request forthe enablement using the first channel.
 42. The apparatus of claim 41,wherein the means for transmitting is further configured to: transmit,to the other apparatus, an identifier (ID) of the apparatus along withthe request.
 43. The apparatus of claim 41, wherein the plurality ofchannels supporting wireless communication comprise a plurality oftelevision white space (TVWS) channels supporting TVWS communication,and wherein enablement for the wireless communication comprisesenablement for the TVWS communication.
 44. The apparatus of claim 43,further comprising: means for receiving, in response to the request, atleast one of a first list of channels of the plurality of TVWS channelsavailable for use by the apparatus, or a second list of channels of theplurality of TVWS channels being in use by a subset of the apparatuses;and means for selecting, from the at least one of first list or secondlist, a second channel for the TVWS communication by the apparatus. 45.The apparatus of claim 44, wherein the means for transmitting is furtherconfigured to: transmit, to the other apparatus, a center frequency anda bandwidth of the second channel.
 46. The apparatus of claim 44,wherein the means for receiving is further configured to: receive, fromthe other apparatus, a message with information about periodicity oftransmitting a contact verification signal (CVS) on the second channel;and receive, with the periodicity, the CVS on the second channel, andthe apparatus further comprising means for continuing the TVWScommunication on the second channel based on reception of the CVS. 47.The apparatus of claim 46, further comprising: means for switching fromthe second channel to the first channel, if the CVS was not received fora period of time, and wherein the means for transmitting is furtherconfigured to transmit, using the first channel, another request for theenablement.
 48. The apparatus of claim 46, wherein the means fortransmitting is further configured to: transmit, on the second channelaccording to the periodicity, one or more traffic indication map (TIM)messages and a delivery traffic indication map (DTIM) message before theCVS was transmitted on the second channel from the other apparatus, andwherein each of the TIM messages comprises a counter that counts down tothe transmission of the DTIM message, and the DTIM message istransmitted immediately before the CVS transmission.
 49. The apparatusof claim 48, wherein the means for transmitting is further configuredto: transmit, upon receiving the CVS, a broadcast message indicatingthat the CVS was transmitted from the other apparatus.
 50. The apparatusof claim 44, wherein the means for receiving is further configured to:receive, from the other apparatus, a message comprising a schedule ofreceiving a contact verification signal (CVS) on the second channel; andreceive the CVS according to the schedule, and the apparatus furthercomprising means for refraining, according to the schedule, from theTVWS communication on the second channel, and means for continuing theTVWS communication on the second channel after receiving the CVS. 51.The apparatus of claim 50, wherein the means for transmitting is furtherconfigured to: transmit, in response to the message, a broadcast messagewith the schedule to one or more of the apparatuses associated with theapparatus.
 52. The apparatus of claim 50, wherein the means fortransmitting is further configured to: transmit a Contention-Free End(CF-End) frame after the CVS was transmitted from the other apparatus.53. The apparatus of claim 50, wherein the means for transmitting isfurther configured to: transmit a Clear-to-send (CTS)-to-Self messageaccording to the schedule, and wherein the CTS-to-Self message comprisesa duration field indicating a period of time equal to at least durationof transmitting the CVS from the other apparatus.
 54. The apparatus ofclaim 43, further comprising: means for receiving, on the first channel,a message with a schedule of transmitting the signal from the otherapparatus, if the first channel is used for the TVWS communication bythe apparatus and a subset of the apparatuses; and means for refrainingfrom the TVWS communication according to the schedule.
 55. The apparatusof claim 54, wherein the means for transmitting is further configuredto: transmit, to one or more apparatuses from the subset associated withthe apparatus, another message with the schedule.
 56. The apparatus ofclaim 54, wherein the means for transmitting is further configured to:transmit a Clear-to-send (CTS)-to-Self message according to theschedule, and wherein the CTS-to-Self message comprises a duration fieldindicating a period of time equal to at least duration of transmittingthe signal from the other apparatus.
 57. The apparatus of claim 39,wherein the means for transmitting is further configured to: transmit abeacon comprising information about the first channel, and wherein theinformation comprises at least one of a center frequency of the firstchannel, a bandwidth of the first channel, or an address of the otherapparatus.
 58. A non-transitory computer-readable medium comprisinginstructions executable to: search, at an apparatus, a plurality ofchannels supporting wireless communication for a signal transmitted fromanother apparatus on a first channel of the channels, wherein the signalis capable of reaching a plurality of apparatuses for advertising anenablement for the wireless communication; detect, based on the search,the signal and the first channel; and transmit, to the other apparatusupon the detection, a request for the enablement using the firstchannel.
 59. An access point, comprising: at least one antenna; a firstcircuit configured to search a plurality of channels supporting wirelesscommunication for a signal transmitted from another access point on afirst channel of the channels, wherein the signal is capable of reachinga plurality of wireless nodes for advertising an enablement for thewireless communication; a second circuit configured to detect, based onthe search, the signal and the first channel; and a transceiverconfigured to transmit, to the other access point upon the detection viathe at least one antenna, a request for the enablement using the firstchannel.
 60. An apparatus for wireless communications, comprising: afirst circuit configured to search a plurality of channels supportingwireless communication for a signal transmitted from another apparatuson a first channel of the channels, wherein the signal is capable ofreaching a plurality of apparatuses for advertising an enablement forthe wireless communication; a transceiver configured to transmit, to theother apparatus using the first channel upon detecting the signal andthe first channel, a request for the enablement, wherein the transceiveris also configured to receive, from the other apparatus in response tothe request, a list of channels of the plurality of channels being inuse by a subset of the apparatuses, and wherein the first circuit isalso configured to search, on channels from the list, for acommunicating apparatus of the subset.
 61. The apparatus of claim 60,wherein the plurality of channels supporting wireless communicationcomprise a plurality of television white space (TVWS) channelssupporting TVWS communication, and wherein enablement for the wirelesscommunication comprises enablement for the TVWS communication.
 62. Theapparatus of claim 61, wherein the transceiver is also configured to:receive, from the other apparatus in response to the request, anotherlist of channels of the plurality of TVWS channels not being in use bythe plurality of apparatuses.
 63. The apparatus of claim 61, furthercomprising: a second circuit configured to perform, upon detecting thecommunicating apparatus, an association procedure with the communicatingapparatus, and wherein the transceiver is also configured to establish,after the association procedure, the TVWS communication with thecommunicating apparatus on a second channel from the list.
 64. Theapparatus of claim 63, wherein the transceiver is also configured to:receive, from the other apparatus, a message with information aboutperiodicity of transmitting a contact verification signal (CVS) on thesecond channel; receive, with the periodicity, the CVS on the secondchannel; and continue the TVWS communication on the second channel basedon reception of the CVS.
 65. The apparatus of claim 64, wherein thetransceiver is also configured to: receive, from the communicatingapparatus, another message comprising a schedule of receiving the CVS onthe second channel; refrain, according to the schedule, from the TVWScommunication on the second channel during reception of the CVS; andreceive the CVS according to the schedule.
 66. The apparatus of claim64, wherein the transceiver is also configured to: receive, from thecommunicating apparatus with the periodicity, a Clear-to-send(CTS)-to-Self message; and refrain, based on the CTS-to-Self message,from the TVWS communication on the second channel during reception ofthe CVS.
 67. The apparatus of claim 64, wherein the transceiver is alsoconfigured to: switch from the second channel to the first channel, ifthe CVS was not received for a period of time; and transmit, to theother apparatus using the first channel, another request for theenablement.
 68. The apparatus of claim 64, wherein the transceiver isalso configured to: receive, on the second channel from thecommunicating apparatus according to the periodicity, one or moretraffic indication map (TIM) messages and a delivery traffic indicationmap (DTIM) message before the CVS was transmitted on the second channelfrom the other apparatus, and wherein each of the TIM messages comprisesa counter that counts down to transmission of the DTIM message from thecommunicating apparatus, and the DTIM message is received immediatelybefore receiving the CVS transmission.
 69. The apparatus of claim 64,wherein the transceiver is also configured to: receive, from thecommunicating apparatus, a Contention-Free End (CF-End) frame after theCVS was transmitted from the other apparatus, and the apparatus furthercomprising a third circuit configured to reset a Network AllocationVector (NAV) counter based on the CF-End frame.
 70. The apparatus ofclaim 61, wherein the transceiver is, upon detecting the communicatingapparatus, also configured to: receive, on the first channel from thecommunicating apparatus, a message with a schedule of transmitting thesignal from the other apparatus, if the first channel is used for theTVWS communication by the apparatus and the communicating apparatus; andrefrain from the TVWS communication according to the schedule.
 71. Theapparatus of claim 61, wherein the transceiver is, upon detecting thecommunicating apparatus, also configured to: receive, on the firstchannel from the communicating apparatus, a Clear-to-send (CTS)-to-Selfmessage transmitted according to a schedule of transmitting the signalfrom the other apparatus, if the first channel is used for the TVWScommunication by the apparatus and the communicating apparatus; andrefrain from the TVWS communication based on the CTS-to-Self message.72. The apparatus of claim 71, wherein: the CTS-to-Self messagecomprises a duration field indicating a period of time equal to at leastduration of transmitting the signal from the other apparatus, and thetransceiver is also configured to refrain from the TVWS communicationfor the period of time.
 73. The apparatus of claim 60, wherein the firstcircuit is also configured to: perform active scanning during the searchfor the communicating apparatus, or perform passive scanning during thesearch for the communicating apparatus.
 74. The apparatus of claim 60,wherein: the signal comprises a direct sequence spread spectrum (DSSS)signal.
 75. The apparatus of claim 60, wherein: a data rate of thesignal is approximately 10 Kbits per second or 100 Kbits per second, anda bandwidth of the signal is approximately 5 MHz or 6 MHz.
 76. Theapparatus of claim 60, wherein: a data rate of the signal isapproximately 250 Kbits per second, 125 Kbits per second, or 62.5 Kbitsper second, and a bandwidth of the signal is approximately 5 MHz. 77.The apparatus of claim 60, wherein the transceiver is also configuredto: receive a beacon comprising information about the first channel, andthe apparatus further comprising a second circuit configured to detectthe signal and the first channel based on the beacon.
 78. The apparatusof claim 77, wherein the information comprises at least one of a centerfrequency of the first channel, a bandwidth of the first channel, or anaddress of the other apparatus.
 79. The apparatus of claim 60, whereinthe transceiver is, upon detecting the communicating apparatus, alsoconfigured to: receive, from the communicating apparatus, aContention-Free End (CF-End) frame after the signal was transmitted fromthe other apparatus, and the apparatus further comprising a thirdcircuit configured to reset a Network Allocation Vector (NAV) counterbased on the CF-End frame.
 80. The apparatus of claim 60, wherein thesignal comprises an Orthogonal Frequency Division Multiplexing (OFDM)signal with repetition codes.
 81. A method for wireless communications,comprising: searching, at an apparatus, a plurality of channelssupporting wireless communication for a signal transmitted from anotherapparatus on a first channel of the channels, wherein the signal iscapable of reaching a plurality of apparatuses for advertising anenablement for the wireless communication; transmitting, to the otherapparatus using the first channel upon detecting the signal and thefirst channel, a request for the enablement; receiving, from the otherapparatus in response to the request, a list of channels of theplurality of channels being in use by a subset of the apparatuses; andsearching, on channels from the list, for a communicating apparatus ofthe subset.
 82. The method of claim 81, wherein the plurality ofchannels supporting wireless communication comprise a plurality oftelevision white space (TVWS) channels supporting TVWS communication,and wherein enablement for the wireless communication comprisesenablement for the TVWS communication.
 83. The method of claim 82,further comprising: receiving, from the other apparatus in response tothe request, another list of channels of the plurality of TVWS channelsnot being in use by the plurality of apparatuses.
 84. The method ofclaim 82, further comprising: performing, upon detecting thecommunicating apparatus, an association procedure with the communicatingapparatus; and establishing, after the association procedure, the TVWScommunication with the communicating apparatus on a second channel fromthe list.
 85. The method of claim 84, further comprising: receiving,from the other apparatus, a message with information about periodicityof transmitting a contact verification signal (CVS) on the secondchannel; receiving, with the periodicity, the CVS on the second channel;and continuing the TVWS communication on the second channel based onreception of the CVS.
 86. The method of claim 85, further comprising:receiving, from the communicating apparatus, another message comprisinga schedule of receiving the CVS on the second channel; refraining,according to the schedule, from the TVWS communication on the secondchannel during reception of the CVS; and receiving the CVS according tothe schedule.
 87. The method of claim 85, further comprising: receiving,from the communicating apparatus with the periodicity, a Clear-to-send(CTS)-to-Self message; and refraining, based on the CTS-to-Self message,from the TVWS communication on the second channel during reception ofthe CVS.
 88. The method of claim 85, further comprising: switching fromthe second channel to the first channel, if the CVS was not received fora period of time; and transmitting, to the other apparatus using thefirst channel, another request for the enablement.
 89. The method ofclaim 85, further comprising: receiving, on the second channel from thecommunicating apparatus according to the periodicity, one or moretraffic indication map (TIM) messages and a delivery traffic indicationmap (DTIM) message before the CVS was transmitted on the second channelfrom the other apparatus, wherein each of the TIM messages comprises acounter that counts down to transmission of the DTIM message from thecommunicating apparatus, and the DTIM message is received immediatelybefore receiving the CVS transmission.
 90. The method of claim 85,further comprising: receiving, from the communicating apparatus, aContention-Free End (CF-End) frame after the CVS was transmitted fromthe other apparatus; and resetting a Network Allocation Vector (NAV)counter based on the CF-End frame.
 91. The method of claim 82, furthercomprising: upon detecting the communicating apparatus, receiving, onthe first channel from the communicating apparatus, a message with aschedule of transmitting the signal from the other apparatus, if thefirst channel is used for the TVWS communication by the apparatus andthe communicating apparatus; and refraining from the TVWS communicationaccording to the schedule.
 92. The method of claim 82, furthercomprising: upon detecting the communicating apparatus, receiving, onthe first channel from the communicating apparatus, a Clear-to-send(CTS)-to-Self message transmitted according to a schedule oftransmitting the signal from the other apparatus, if the first channelis used for the TVWS communication by the apparatus and thecommunicating apparatus; and refraining from the TVWS communicationbased on the CTS-to-Self message.
 93. The method of claim 92, wherein:the CTS-to-Self message comprises a duration field indicating a periodof time equal to at least duration of transmitting the signal from theother apparatus, and the method further comprising refraining from theTVWS communication for the period of time.
 94. The method of claim 81,further comprising: performing active scanning during the search for thecommunicating apparatus, or performing passive scanning during thesearch for the communicating apparatus.
 95. The method of claim 81,wherein: the signal comprises a direct sequence spread spectrum (DSSS)signal.
 96. The method of claim 81, wherein: a data rate of the signalis approximately 10 Kbits per second or 100 Kbits per second, and abandwidth of the signal is approximately 5 MHz or 6 MHz.
 97. The methodof claim 81, wherein: a data rate of the signal is approximately 250Kbits per second, 125 Kbits per second, or 62.5 Kbits per second, and abandwidth of the signal is approximately 5 MHz.
 98. The method of claim81, further comprising: receiving a beacon comprising information aboutthe first channel; and detecting the signal and the first channel basedon the beacon.
 99. The method of claim 98, wherein the informationcomprises at least one of a center frequency of the first channel, abandwidth of the first channel, or an address of the other apparatus.100. The method of claim 81, further comprising: upon detecting thecommunicating apparatus, receiving, from the communicating apparatus, aContention-Free End (CF-End) frame after the signal was transmitted fromthe other apparatus; and resetting a Network Allocation Vector (NAV)counter based on the CF-End frame.
 101. The method of claim 81, whereinthe signal comprises an Orthogonal Frequency Division Multiplexing(OFDM) signal with repetition codes.
 102. An apparatus for wirelesscommunications, comprising: means for searching a plurality of channelssupporting wireless communication for a signal transmitted from anotherapparatus on a first channel of the channels, wherein the signal iscapable of reaching a plurality of apparatuses for advertising anenablement for the wireless communication; means for transmitting, tothe other apparatus using the first channel upon detecting the signaland the first channel, a request for the enablement; means forreceiving, from the other apparatus in response to the request, a listof channels of the plurality of channels being in use by a subset of theapparatuses; and means for searching, on channels from the list, for acommunicating apparatus of the subset.
 103. The apparatus of claim 102,wherein the plurality of channels supporting wireless communicationcomprise a plurality of television white space (TVWS) channelssupporting TVWS communication, and wherein enablement for the wirelesscommunication comprises enablement for the TVWS communication.
 104. Theapparatus of claim 103, wherein the means for receiving is furtherconfigured to: receive, from the other apparatus in response to therequest, another list of channels of the plurality of TVWS channels notbeing in use by the plurality of apparatuses.
 105. The apparatus ofclaim 103, further comprising: means for performing, upon detecting thecommunicating apparatus, an association procedure with the communicatingapparatus; and means for establishing, after the association procedure,the TVWS communication with the communicating apparatus on a secondchannel from the list.
 106. The apparatus of claim 105, wherein themeans for receiving is further configured to: receive, from the otherapparatus, a message with information about periodicity of transmittinga contact verification signal (CVS) on the second channel; and receive,with the periodicity, the CVS on the second channel, and the apparatusfurther comprising means for continuing the TVWS communication on thesecond channel based on reception of the CVS.
 107. The apparatus ofclaim 106, wherein the means for receiving is further configured to:receive, from the communicating apparatus, another message comprising aschedule of receiving the CVS on the second channel; and receive the CVSaccording to the schedule, and the apparatus further comprising meansfor refraining, according to the schedule, from the TVWS communicationon the second channel during reception of the CVS.
 108. The apparatus ofclaim 106, wherein the means for receiving is further configured to:receive, from the communicating apparatus with the periodicity, aClear-to-send (CTS)-to-Self message, and the apparatus furthercomprising means for refraining, based on the CTS-to-Self message, fromthe TVWS communication on the second channel during reception of theCVS.
 109. The apparatus of claim 106, further comprising: means forswitching from the second channel to the first channel, if the CVS wasnot received for a period of time, wherein the means for transmitting isfurther configured to transmit, to the other apparatus using the firstchannel, another request for the enablement.
 110. The apparatus of claim106, wherein the means for receiving is further configured to: receive,on the second channel from the communicating apparatus according to theperiodicity, one or more traffic indication map (TIM) messages and adelivery traffic indication map (DTIM) message before the CVS wastransmitted on the second channel from the other apparatus, and whereineach of the TIM messages comprises a counter that counts down totransmission of the DTIM message from the communicating apparatus, andthe DTIM message is received immediately before receiving the CVStransmission.
 111. The apparatus of claim 106, wherein the means forreceiving is further configured to: receive, from the communicatingapparatus, a Contention-Free End (CF-End) frame after the CVS wastransmitted from the other apparatus, and the apparatus furthercomprising means for resetting a Network Allocation Vector (NAV) counterbased on the CF-End frame.
 112. The apparatus of claim 103, wherein themeans for receiving is, upon detecting the communicating apparatus,further configured to: receive, on the first channel from thecommunicating apparatus, a message with a schedule of transmitting thesignal from the other apparatus, if the first channel is used for theTVWS communication by the apparatus and the communicating apparatus, andthe apparatus further comprising means for refraining from the TVWScommunication according to the schedule.
 113. The apparatus of claim103, wherein the means for receiving is, upon detecting thecommunicating apparatus, further configured to: receive, on the firstchannel from the communicating apparatus, a Clear-to-send (CTS)-to-Selfmessage transmitted according to a schedule of transmitting the signalfrom the other apparatus, if the first channel is used for the TVWScommunication by the apparatus and the communicating apparatus, and theapparatus further comprising means for refraining from the TVWScommunication based on the CTS-to-Self message.
 114. The apparatus ofclaim 113, wherein: the CTS-to-Self message comprises a duration fieldindicating a period of time equal to at least duration of transmittingthe signal from the other apparatus, and the apparatus furthercomprising means for refraining from the TVWS communication for theperiod of time.
 115. The apparatus of claim 102, further comprising:means for performing active scanning during the search for thecommunicating apparatus, or means for performing passive scanning duringthe search for the communicating apparatus.
 116. The apparatus of claim102, wherein the means for receiving is further configured to: receive abeacon comprising information about the first channel, and the apparatusfurther comprising means for detecting the signal and the first channelbased on the beacon.
 117. The apparatus of claim 116, wherein theinformation comprises at least one of a center frequency of the firstchannel, a bandwidth of the first channel, or an address of the otherapparatus.
 118. The apparatus of claim 102, wherein the means forreceiving is, upon detecting the communicating apparatus, furtherconfigured to: receive, from the communicating apparatus, aContention-Free End (CF-End) frame after the signal was transmitted fromthe other apparatus, and the apparatus further comprising means forresetting a Network Allocation Vector (NAV) counter based on the CF-Endframe.
 119. The apparatus of claim 102, wherein the signal comprises anOrthogonal Frequency Division Multiplexing (OFDM) signal with repetitioncodes.
 120. A non-transitory computer-readable medium comprisinginstructions executable to: search, at an apparatus, a plurality ofchannels supporting wireless communication for a signal transmitted fromanother apparatus on a first channel of the channels, wherein the signalis capable of reaching a plurality of apparatuses for advertising anenablement for the wireless communication; transmit, to the otherapparatus using the first channel upon detecting the signal and thefirst channel, a request for the enablement; receive, from the otherapparatus in response to the request, a list of channels of theplurality of channels being in use by a subset of the apparatuses; andsearch, on channels from the list, for a communicating apparatus of thesubset.
 121. An access terminal, comprising: at least one antenna; afirst circuit configured to search a plurality of channels supportingwireless communication for a signal transmitted from an access point ona first channel of the channels, wherein the signal is capable ofreaching a plurality of wireless nodes for advertising an enablement forthe wireless communication; a transceiver configured to transmit, viathe at least one antenna to the access point using the first channelupon detecting the signal and the first channel, a request for theenablement, wherein the transceiver is also configured to receive, viathe at least one antenna from the access point in response to therequest, a list of channels of the plurality of channels being in use bya subset of the wireless nodes, and wherein the first circuit is alsoconfigured to search, on channels from the list, for another accesspoint of the subset.